Browsing by Author "Olson, Sandra L."
Now showing 1 - 4 of 4
- Results Per Page
- Sort Options
Item Applying Flammability Limit Probabilities and the Normoxic Upward Limiting Pressure Concept to NASA STD-6001 Test 1(44th International Conference on Environmental Systems, 2014-07-13) Olson, Sandra L.; Beeson, Harold; Fernandez-Pello, A. CarlosRepeated Test 1 extinction tests near the upward flammability limit are expected to follow a Poisson process trend. This Poisson process trend suggests that rather than define a ULOI and MOC (which requires two limits to be determined), it might be better to define a single upward limit as being where 1/e (where e (=~2.7183) is the characteristic time of the normalized Poisson process) of the materials burn, or, rounding, where approximately 1/3 of the samples fail the test (and burn). Recognizing that spacecraft atmospheres will not bound the entire oxygen-pressure parameter space, but actually lie along the normoxic atmosphere control band, we can focus the materials flammability testing along this normoxic band. A Normoxic Upward Limiting Pressure (NULP) is defined that determines the minimum safe total pressure for a material within the constant partial pressure control band. Then, increasing this pressure limit by a factor of safety, we can define the material as being safe to use at the NULP + SF (where SF is on the order of 10 kPa, based on existing flammability data). It is recommended that the thickest material to be tested with the current Test 1 igniter should be 3 mm thick (1/8”) to avoid the problem of differentiating between an ignition limit and a true flammability limit.Item Experimental Results on the Effect of Surface Structures on the Flame Propagation Velocity of PMMA in Microgravity(47th International Conference on Environmental Systems, 2017-07-16) Eigenbrod, Christian; Hauschildt, Jakob; Meyer, Florian; Urban, David L.; Ruff, Gary A.; Olson, Sandra L.; Ferkul, Paul; Jomaas, Grunde; Toth, BalazsMaterials foreseen for the design of manned spacecraft must pass the NASA-STD 6001B Test 1 regarding its fire hazard. During this qualification test in 1g conditions, a flat sample with fire protected edges is placed vertically in a quiescent environment, and ignited at its lower end. To pass the test, it must extinguish within 150 mm propagation length. Even though PMMA does not pass this test, it is extensively used for scientific investigations because of its repeatability and use in previous studies. Systematic ground tests of generic geometries have revealed that almost any realistic machined geometry like sharp or rounded edges, fins or grooves may lead to a rise in flame propagation velocity up to a factor of four related to the flat standard sample. For the first time, the flamed spread over a structured, thick PMMA sample of 290 x 50 mm was examined in microgravity (3x10-5g0) under concurrent flow of 0.20 m/s onboard Orbital ATK’s re-supply spacecraft Cygnus. The results were compared to the behavior of a similarly-sized flat sample. Just as in 1g, it was found that vertical structures promote faster flame spread compared to a flat sample but to a lesser degree than what is observed in 1g. While the structured sample burned 70% faster than the flat sample in 1g, this difference was reduced to only 32% in microgravity. Both samples burned drastically slower in microgravity: 23 times slower for the structured sample and 18 times slower for the flat sample. In 1g the pyrolysis front rapidly spreads along the surface and takes advantage of improver in depth heat transfer afforded by edges but, in microgravity, the burning mostly confined to the leading edge which has the best supply of oxygen. Finally, the microgravity flames produced more smoke and exhibited a larger preheat area.Item Overview of the “Solid Combustion” Experiment in the Japanese Experiment Module “Kibo” on the International Space Station(45th International Conference on Environmental Systems, 2015-07-12) Kikuchi, Masao; Fujita, Osamu; Takahashi, Shuhei; Ito, Akihiko; Torikai, Hiroyuki; Nakamura, Yuji; Olson, Sandra L.Fire safety in human-rated spacecraft or space station is one of the most important requirements for any human space mission. To prevent fires in space, material flammability tests such as NASA-STD-6001B standards have been widely employed. The tests are performed in a normal gravity environment. Previous research showed material flammability could be higher in microgravity environments for some conditions, so it is important to understand the impact of gravity-induced buoyant flow on material flammability. In 2010, the investigation titled “Quantitative Description of Gravity Impact on Solid Material Flammability as a base of Fire Safety in Space (Solid Combustion)” was selected by the Japan Aerospace Exploration Agency (JAXA) as an experiment candidate in the Japanese Experiment Module “Kibo” on the International Space Station (ISS). In the “Solid Combustion” experiment, three types of solid material (polyethylene insulated wires, thin PMMA sheets and thin filter papers) are selected as test samples. Flammability of these materials will be quantitatively determined in microgravity by evaluating the limits of two fundamental processes of solid combustion, which are (1) ignition limit of the solid material, and (2) flame spread limit (extinction limit) over the solid material. It is expected that the evaluation of the discrepancy between the data in normal gravity and microgravity will lead to improved understanding of the level of the conservatism of the existing material flammability tests. Also, a “material flammability map” for the selected samples will be produced as a fire safety database for spacecraft, which will be reference data to estimate the flammability of other solid materials. To date, a detailed consideration of the experimental plan in orbit and a conceptual design of the experiment specific hardware to be installed into the Multi-purpose Small Payload Rack (MSPR) in the Kibo, have been performed. In this paper, an overview of the “Solid Combustion” experiment and the current status of the project will be presented.Item Results from on-board CSA-CP and CDM Sensor Readings during the Burning and Suppression of Solids – II (BASS-II) Experiment in the Microgravity Science Glovebox (MSG)(45th International Conference on Environmental Systems, 2015-07-12) Olson, Sandra L.; Ferkul, Paul V.; Bhattacharjee, Subrata; Miller, Fletcher J.; Fernandez-Pello, Carlos; Link, Shmuel; T'ien, James S.; Wichman, IndrekFor the first time on ISS, BASS-II utilized MSG working volume dilution with gaseous nitrogen (N2). We developed a perfectly stirred reactor model to determine the N2 flow time and flow rate to obtain the desired reduced oxygen concentration in the working volume for each test. We calibrated the model with CSA-CP oxygen readings offset using the Mass Constituents Analyzer reading of the ISS ambient atmosphere data for that day. This worked out extremely well for operations, and added a new vital variable, ambient oxygen level, to our test matrices. The main variables tested in BASS-II were ambient oxygen concentration, ventilation flow velocity, and fuel type, thickness, and geometry. BASS-II also utilized the on-board CSA-CP for oxygen and carbon monoxide readings, and the CDM for carbon dioxide readings before and after each test. Readings from these sensors allow us to evaluate the completeness of the combustion. The oxygen and carbon dioxide readings before and after each test were analyzed and compared very well to stoichiometric ratios for a one step gas-phase reaction. The CO versus CO2 followed a linear trend for some datasets, but not for all the different geometries of fuel and flow tested. We calculated the heat release rates during each test from the oxygen consumption and burn times, using the constant 13.1 kJ of heat released per gram of oxygen consumed. The results showed that the majority of the tests had heat release rates well below 100 Watts. Lastly, the global equivalence ratio for the tests is estimated to be fuel rich: 1.3 on average using mass loss and oxygen consumption data.